## Verifying the concentration of your Sodium Hydroxide solution

OK, so you have some Sodium Hydroxide (NaOH) solution that you have been using to measure your sake or wine’s acidity but it has been a while. Maybe even a long while. You want to make a measurement but will it be accurate? Will it have absorbed too much CO2 to give an accurate measure? How do you know? Well, with a dilute solution of Hydrochloric acid (HCl), 0.1 molarity is good, you can answer your questions and get back to the task at hand.

Unlike Sodium Hydroxide, Hydrochloric acid is stable so it can be stored and used over a long period without degradation. This stability makes HCl ideal for determining the actual concentration of your NaOH solution.

Using HCl to determine the concentration of NaOH depends on the reaction:

which converts an acid and a base to water and a salt. This reaction along with the following equality can be used to determine the actual concentration of the NaOH solution if we have accurate knowledge about the other values.

Knowing the HCl solution molarity (0.1 for our work) and using a specific sample volume of the HCl solution (say 10ml) along with the fact that the molar ratio1 in the above reaction is 1:1 leaves only the NaOH volume to be determined in order to calculate the NaOH concentration. Let sample1 be the HCl and sample2 be the NaOH. This gives:

so

or

Given this, if we titrate to neutralize 10ml of a 0.1 Molarity solution of HCl and it takes 11ml of your NaOH solution to neutralize the HCl then the molarity of the NaOH solution is 0.0909… M or about 0.091 M. Now that you know the molarity of the NaOH solution that you are using, you can substitute this value into the equation you are using to determine the acidity of your sake while following the standard titration procedure.

One additional benefit of being able to determine the molarity of your NaOH solution is that you can actually make your own. With this you are no longer dependent on your lab supply store for NaOH solutions with an accurately known molarity. The mole mass of NaOH is roughly 40 grams. So to create a 0.1 molarity solution of NaOH we start with 1 liter of distilled water and add 4 grams (0.1 x 40) of NaOH granules. This gets us very close to the 0.1 molarity solution we want but with the accuracy of our equipment it is not close enough. With the above procedure we can get the needed accuracy.